This invention relates to computer database systems generally and more particularly to computer database systems for use in process monitoring of various manufacturing operations, and the like. The invention particularly relates to such systems which seek to store and retrieve in a coordinated fashion sets of data within predetermined time constraints on either an as-requested basis or on a continuous event driven basis.
Database systems generally comprise a collection of data stored in various files, records, and fields, together with certain dictionaries, indexes, and the like, to permit quick and easy storage and access of the information within the database. In most contemporary database systems, each type or class of data is stored in a separate file with an appropriate index such that the logical intersection of the data from two separate files may be examined by asking an appropriate query of the database. The computer system then examines each database in turn, extracting the required information from each database, which extracted information is then assembled in a correlated fashion for presentation in response to that inquiry. As a general rule, the time for response to the query is directly related to the number of files which have to be examined or searched for the information and the length of each file. If the files are indexed or otherwise ordered in a sequence based on a criteria of the data stored in the file, then the access time can be reduced significantly within each file. Nevertheless, the coordination of the data from several files will still depend on a need to examine each file in order to retrieve the necessary information.
The storage of information in such general database files is also related to their size and structure. While it is readily apparent that data could quickly be added to any file in random order, in the absence of some indexing method, retrieval of that same data from that file would require an examination of the entire file. If, on the other hand, either the file itself is organized in some sequential or an index is provided which allows the sequential order of the file to be established, then the time to enter data into the appropriate location or generate the appropriate index necessarily increases the time necessary to enter information into the file. As a general rule, the data itself is rarely placed in an ordered arrangement while the use of indexing arrangements is widely used. Nevertheless, the index in each given file is generally separate from and has no relationship to any other file maintained by the database at the same time and thus the correlation of information from two files requires an independent search of each of the indexes employed in each of the files into which access is required in order to retrieve information from multiple files.
The need to generate multiple indexes in order to deposit related information into multiple files of a single database and, perhaps more importantly, the need to search multiple indexes in order to retrieve related information from multiple files of a single database significantly slows the operation of a database. While in most circumstances such access and retrieval delays are tolerable, they cannot be tolerated in data processing systems which are employed in real time critical path problems such as process monitoring systems employed in connection with various manufacturing operations. That is, it is necessary that any computer based process monitoring system used for monitoring a manufacturing operation must at all times be able to operate faster than the underlying manufacturing operation which it is tasked to monitor. From a practical point of view, manufacturers cannot tolerate a situation where a manufacturing process is being slowed as a result of the inability of a computer to keep up with the informational requirements of that manufacturing process.
Thus a central problem sought to be solved by the present invention is the development of a database which can in each and every circumstance complete a data access and retrieval operation which, even under the worst case, operates within a well-defined and known upper limit of time which upper limits can be employed to ensure that all necessary data recording and analysis can be achieved within the time constraints imposed by the external manufacturing process which the system is monitoring. It will be readily appreciated of course that such a database organization has wide utilization even beyond manufacturing process monitoring and has particular utility in any circumstance where it is desirable that a database be sufficiently fast to operate within the time constraints of events external to that database so long as they are not beyond the capacity of the computer hardware in which the database management system is installed which is of course always a limiting factor.